1. Field of the Invention
This invention relates to a process for separating at least two hydrate forming gases in a gas mixture from each other. More particularly, this invention relates to a process for separating carbon dioxide and methane present in a gas mixture from each other.
2. Description of Related Art
High concentrations (greater than about 70% by volume) of carbon dioxide exist in large natural gas reservoirs, such as Moxa Arch in the Rocky Mountain region of the United States. In addition, natural gas produced from coal beds, that is, “coal bed methane”, also has high concentrations of carbon dioxide. In both instances, it is necessary to remove the carbon dioxide prior to delivering the natural gas to a pipeline. As a result, this natural gas cannot be produced economically in the former case because of the high gas processing costs associated therewith, and, in the latter case, the costs of production are high.
Several processes have been proposed for addressing the issue of removing CO2 from natural and other gases including the Ryan Holmes process, amine scrubbing, cellulose acetate membranes, controlled freeze zone process approach, carbon dioxide crystallization, and application of physical solvents. However, at least some of these processes are typically not suitable for processing streams in which high concentrations of carbon dioxide are present in association with other natural gas components such as methane and ethane. For example, gas streams comprising low concentrations of carbon dioxide, in the range of about 10–20% by volume, may be effectively treated using amines, and gas streams comprising medium concentrations of carbon dioxide, in the range of about 20–30% by volume, may be effectively treated using physical solvents such as methanol. However, physical solvent processes require a suitably high pressure in association with a suitably high concentration of the component to be removed, such that the product of the concentration and the pressure is a suitably high “partial pressure”. Furthermore, conventional amine and physical solvent processes, even if operated at pressure, generally produce the captured, carbon dioxide-enriched stream at low pressure as necessitated by the conditions required to regenerate the amine or physical solvent stream for reuse.